Conventionally, for example, a grinding stone has been available that grinds the journal, the crank pin or the like of a vehicular crank shaft (see Patent Document 1 shown below). On the grinding stone disclosed in Patent Document 1, two kinds of grinding layers having different properties are provided in a state of being divided in chips on the outer peripheral surface of a disc-like member forming the grinding wheel. Specifically, on the angular portions at both ends of the outer peripheral surface of the disc-like member in the direction of the rotation axis, since a high grinding resistance is caused at the time of grinding, a grinding layer that is formed of abrasive grains with a large grain diameter and resistant to wear is provided. Moreover, on the cylindrical portion between the angular portions at both ends of the outer peripheral surface, since no high grinding resistance is caused, a grinding layer that is formed of abrasive grains having a small grain diameter and being prone to wear and where a high finishing accuracy is expected is provided. However, in the above, since the grinding layer that is resistant to wear and the grinding layer that is prone to wear adjoin in the axial direction and grinding work is performed at the same time, the degree of wear is different between the grinding layers, so that a level difference is caused at the boundary portions. For this reason, there is a possibility that this level difference is transferred to the workpiece to deteriorate the finishing accuracy.
Accordingly, on the grinding stone of Patent Document 1, the boundary portions in the axial direction formed of the two kinds of grinding chips are not provided with a continuous straight line form as shown in FIG. 6 in the circumferential direction of the outer peripheral surface but are arranged in a so-called staggered form where they are staggered one by one as shown in FIG. 3. This suppresses the occurrence of a large level difference at the boundary portions between the grinding layer that is resistant to wear and the grinding layer that is prone to wear, which suppresses the occurrence of a level difference transferred to the workpiece.